The navigation information comes from one or several satellites belonging to a global navigation satellite system (GNSS).
There are currently several GNSS systems, which in particular include the GPS system, the GLONASS system and the GALILEO system, which is expected to be brought online soon.
In general, a GNSS system is made up of a plurality of satellites emitting navigation information in the form of electromagnetic signals toward the Earth's surface.
The receiver is then able to receive these electromagnetic signals to extract the corresponding navigation information therefrom and, by analyzing navigation information from several satellites, to determine a navigation solution.
Such a navigation solution in particular includes the position of the receiver in a land reference, its speed and the time synchronized with the corresponding GNSS system.
The reception of the electromagnetic signals from the satellites can be prevented or disrupted by the presence of disturbance signals of various natures.
These disturbance signals in particular include malevolent signals aiming to scramble “pure” signals coming from satellites of the corresponding GNSS system and to thereby compromise the determination of the position by the receiver.
Some of these signals are similar to the signals emitted by the GNSS system and make it possible to deceive the receiver by causing it to determine a deliberately erroneous navigation solution.
In order to avoid these situations, some receivers make it possible to detect a “deception” situation, i.e., the presence of one or several malevolent signals near the receiver.
According to the state of the art, the detection of deception situations is based primarily on methods for verifying the consistency between the signals received by the receiver and secure information, i.e., information coming from a reliable source.
The secure information must then be known a priori by the receiver and for example comprise the speed of the receiver, the time or, at least partially, its position.
However, in general, this information cannot be known by the receiver when it is started cold. Starting cold thus refers to the state of the receiver in which no secure information is known by it. This state corresponds to the state of the receiver just after it is turned on.
For such a type of receivers, it is therefore necessary to provide at least one piece of secure information when they are started cold so that a deception situation can be detected.
One can thus see that this requires major operational constraints for the operation of this type of receiver.